The present invention relates to a magnetic disk cartridge and, more particularly, to a magnetic disk cartridge which prevents the formation of a gap between upper and lower shells in the rear end portion of the cartridge case.
Generally, a 3.5-inch micro floppy disk (hereinafter referred to as a 3.5-inch MFD) includes a cartridge case composed of upper and lower shells, a magnetic disk rotatably received within the case, and a liner and a lifter for pressing the liner toward the magnetic disk and disposed on the inner wall surface of the case. A window is formed in the cartridge case for recording and reproduction from the magnetic disk. A shutter is slidably fitted to the outside of the case for opening and closing the window. The cartridge case, which is generally square in shape, is normally formed by upper and lower shells formed of synthetic resin placed in opposition to one another, with respective corner portions of the case spot welded to one another to thereby form an integral structure.
In the conventional magnetic disk cartridge, in order to facilitate production and to improve the overall structure of the cartridge, the sides 1, 2, 3 and 4, which are the abutted portions of the peripheral edges of the upper shell A (FIG. 11) and the lower shell B (FIG. 12), are not welded together along their entire lengths, but only the corner portions thereof are welded together. That is, in the upper and lower shells A and B shown in FIG. 11 and 12, after a liner and the like (not shown) are mounted to each of the shells and a magnetic disk is placed between the upper and lower shells A and B, welding projections a.sub.1 and a.sub.2, b.sub.1 and b.sub.2, c.sub.1 and c.sub.2, and d.sub.1 and d.sub.2, which are formed in the respective corner portions of the upper and lower shells A and B in respective opposing positions, are abutted against each other simultaneously as the upper and lower shells are accurately superimposed on each other, and the welding projections are then welded together using ultrasonic welding.
As described above, due to the fact that the entirety of the case peripheral edges are not welded, there is a possibility that a small gap can be formed between the unwelded portions between the upper and lower shells A and B. Especially there is a marked tendency of such a gap occurring in the case rear portion (on the side opposite the window 9) where the shutter is not present.
When the atmospheric air is dry, the amount of static electricity charge carried by a user can be quite high. Under such conditions, when the user touches the cartridge in order to load or unload the cartridge, the static electric can be discharged between the user's hand and the magnetic disk through the gap between the shells, which can damage the magnetic disk or cause dielectric breakdown of the insulation of the wires of a magnetic head. Also, if dust or other foreign matter enters through the gap, the rotating magnetic disk can be damaged.
On the other hand, if the entire peripheries of the shells are welded together in order to prevent the above-mentioned problems, the welded peripheries can be distorted due to the expansion and contraction thereof caused by varying temperatures, which can twist the whole of the cartridge, with the result that the cartridge cannot be loaded accurately.
In view of the above-mentioned problems, in Japanese Utility Model Publications Nos. Sho. 60-180377 and 62-42172, there is disclosed a cartridge in which at least the vicinity of the central portion of the rear edge portion of the case or substantially the whole of the rear edge portion is welded. However, it has been found that it is difficult to precisely balance the welded portions, a gap can easily be formed in the right and left sides of the case which are not welded, the case is easily distorted due to temperature changes, and the welding operation is often difficult to control.